A microcosm system to evaluate the fate of 14C labelled pesticides in soils from different climate zones

A method for quantifying and comparing the processes relevant to the fate of pesticides in soils from various climate zones - volatilization, mineralization, transport and leaching - was developed. A microcosm, consisting of an undisturbed soil column in a round metal cylinder (height 30 cm, 15 cm inner diameter), is fitted with devices to collect and analyze the leachate and to investigate the gas phase above the soil surface. To include all the conversion products in the investigations, 14C labelled pesticides are used. Thus, determination of the complete 14C mass balance is possible. As the first model herbicide, 14C-terbuthylazine was used. Ventilation was based on a wind speed of 1 m/s; irrigation, based on an average rainfall of 600 mm/a, was applied discontinuously, interrupted by dry periods. Soils from Brazil, China and Germany were investigated in four replicates each. Soil from Brazil, with the highest organic matter and clay contents, exhibited the lowest volatilization of 14C-terbuthylazine, the highest mineralization to 14CO2, the lowest vertical transport and the lowest leaching of 14C into the percolate water, followed by the soils from China and Germany. Soil from Germany showed the highest volatilization, the highest vertical transport and the highest leaching rates. These findings demonstrate that the properties of soils, as formed under different climatic conditions, influence the fate and persistence of a pesticide in the soil environment. (author). 5 refs, 1 fig., 3 tabs